You get this achievement by completing the 11th mission of the campaign on any difficulty.
The mission is fairly strait forward aside from a couple tricky parts:
-mid way
*** Spoiler - click to reveal ***There's a spot about half way with mortar fire raining down on the squad. Run from cover to cover and wait for the shells to land between each and it's not bad.
-Near the end
*** Spoiler - click to reveal ***You'll need to walk down a corridor and when you do so a flaming truck comes barreling down on you from the other end. When you jump down into the corridor you need to knife the grate on the ground, jump into the opening you've made and crouch. I died a number of times before figuring this out.
This is a good mission to rack up some sniper kills if you haven't already gotten the achievement "Sniper Rifle Strike" (Campaign: 50 kills with sniper rifles)
Happy hunting! =]